1. Field of the Invention
The present invention comprises an apparatus and methods for a human extender. In particular, the invention relates to an apparatus and methods for a human extender controller capable of interfacing a human operator and a physical object so that the physical object can be dexterously manipulated.
2. Background Art
A human extender is a device that amplifies the lifting capacity of a human operator and allows a preselected amount of force feedback to the operator (i.e., the operator can feel part of the load). This type of system is fundamentally different from a teleoperator system because the master and slave manipulators are a single unit in a human extender. This concept was first developed in the 1960's by General Electric during the Hardiman project, as documented in the publications of "Special Interim Study, Hardiman I Prototype Project," Report S-68-1060, General Electric Company, Schenectady, N.Y., Apr. 19, 1968, "Hardiman I Arm Test, Hardiman I Prototype Project," Report S-70-1019, General Electric Company, Schenectady, N.Y., Dec. 31, 1969, and "Final Report on Hardiman I Prototype for Machine Augmentation of Human Strength and Endurance," General Electric Company, Schenectady, N.Y., Aug. 30, 1971. More recently, Kazerooni disclosed a scaled down version of a similar concept in the papers of "Human/Robot Interaction via the Transfer of Power and Information, Part I: Dynamics and Control Analysis," Kazerooni, H., EKE Robotic and Automation Conference, pp. 1632-1640 (Scottsdale, Ariz., 1989), "Human/Robot Interaction via the Transfer of Power and Information, Part 2: An Experimental Analysis," Kazerooni, H., EKE Robotic and Automation Conference, pp. 1641-1647 (Scottsdale, Ariz., 1989), "Human-Robot Interaction via the Transfer of Power and Information Signal," Kazerooni, H., EKE Transaction on Systems, Man, and Cybernetics, Vol. 20, No. 2, pp. 450-463 (1990), and "Human Extenders," Kazerooni, H., J. Guo, Journal of Dynamic Systems, Measurement, and Control, Vol. 115, pp. 281-290 (1990).
The human extender concept is developed in order to take benefit from the strength advantage of robot manipulators and the intellectual advantage of human beings. Numerous human activities require human operators performing tasks that demand their intelligence and physical strength often beyond their capability. These tasks cannot be best performed by a traditional robot manipulator because these tasks need a spontaneous information signal and power transfer between the human operator and the working environment, which cannot be provided by the traditional robot manipulator with a master-slave design. In contrast, force reflection occurs naturally in a human extender. Without a separate set of actuators, the human hand feels the actual forces on the extender, both direction of motion and a scaled-down version of the load. For example, if a human extender manipulates a 500 lbs. object, the human operator may just feel 10 lbs. while the extender supports the rest of the load. This 10 lbs. contact forces are used not only for manipulation of the object, but also for generating the appropriate signals to the extender controller. The capability of a human extender is often measured by its force reflection ratio, which is defined as the ratio of the real load to the forces the human feels. For the example just given, the force reflection ratio is 50 to 1.
Many potential uses are available for human extender. For example, in an unstructured environment, military personnel often need to use special equipment such as weapon loader to manipulate and orient large objects. An equipment capable of transmitting back to the operator a fraction of the object's dynamics (e.g., its weight, contact forces, inertia, slippage, etc.) could significantly enhance productivity, quality, and safety. A human extender can be integrated into a weapon loader to perform such tasks.
Similarly, a human extender can find a wide area of civic use in fields such as the package-delivery service industry. Package-delivery companies, such as United Parcel Service of America, Inc. (UPS), have increased their weight limit on the boxes they carry gradually. UPS has gone from 70 pounds to 150 pounds in order to remain competitive. UPS has also experience a 2 to 3% higher lost time due to injuries than similar types of businesses. A typical job at a UPS hub requires lifting and sorting up to 900 boxes an hour and placing them on a dozen conveyor belts. A dextrous device that has a large work space and can handle large payloads, while utilizing the intelligence of the operator to spontaneously generate the command signal to handle the loads repeatedly, safely, accurately and efficiently, could have a significant impact in the package-delivery service industry. Similar devices can find their use in manufacture assembly lines, in rescue operations, in construction industry and many other areas.
However, a number of problems associated with the available human amplifier systems. Profound instabilities due to gross nonlinearities in the fluid power system (e.g., nonlinear pressure-flow relationship, time varying fluid properties, large quantities of nonlinear friction, time varying system dynamics) and differences in human operator dynamics rendered the system impractical for large force gains as discussed in the paper of "Human-Robot Interaction via the Transfer of Power and Information Signal," Kazerooni, H., EKE Transaction on Systems, Man, and Cybernetics, Vol. 20, No. 2, pp. 450-463 (1990). These instabilities occur when the human extender makes contact with the environment. To overcome these instabilities, a computed torque technique was used with a proportional plus derivative law ("PD") controller as the primary stabilizing controller as disclosed in the paper of "Human Extenders," Kazerooni, H., J. Guo, Journal of Dynamic Systems, Measurement, and Control, Vol. 115, pp. 281-290 (1990). Unfortunately, computed torque technique is a model based scheme that requires significant knowledge about the physical system plus it represents a significant computational burden on the controller. Computed torque can be rendered basically useless if the model is just a few percent off of the calculated value. Because of these problems, the current human extenders have very limited payload capacities and limited force reflection ratios under 19 to 1 as discussed in the paper "Human Extenders," Kazerooni, H., J. Guo, Journal of Dynamic Systems, Measurement, and Control, Vol. 115, pp. 281-290 (1990).
A one-axis human amplifier system is described in U.S. Pat. No. 5,865,426 issued to Kazerooni. Upward vertical forces such as gravity and inertia are reduced to the human operator through this system when picking up a load such as a heavy box. The load is attached to a single actuator through a wire rope. Since wire rope can react only to tension type loads this system is suitable for lifting objects only in the upward vertical direction. This system is deficient for tasks that require forces in both the upward and downward directions or if forces and moments are required in other planes of motion.
Moreover, recent development in military loading and reloading devices invites the improvement of human extenders. Present reloading devices consist of a family of mobile heavy hydraulic lifters called the Jammer. Although very well designed, the Jammer systems require a three-person crew and for certain loading conditions the turn-around time can sometimes rise dramatically. To reduce the crew size by one and to reduce the overall reloading times, the USAF Air Combat Command is investigating improved weapons loading equipment and techniques. A seven degree-of-freedom system on top of an omni-directional platform has been recently built for the Air Force as part of the Next Generation Munitions Handler Initiative (NGMH). The NGMH is a hydraulically powered manipulator and vehicle intended for dexterously manipulation of missiles and bombs or other materials (e.g., fuel tanks) on various aircraft in the Air Force arsenal. The NGMH has been built to move objects weighing from 200 lbs. to 2000 lbs. while having a position resolution of less than 1 mm. Furthermore, the NGMH has incorporated the human extender concept into its operating system. As a result, the NGMH can amplify the lifting capacity of a person and allow a preselected amount of force feedback to the operator (i.e., the operator can feel part of the reaction load plus his/her forces are amplified to the object). A wide range of force reflection ratios (1 to over 500) with sub millimeter positioning accuracies have been achieved. This development, combined with the instability problem associated with the current available human extender system, has prompted further investigation of new approaches to insure stability when the human extender makes contact with the environment and to design a human extender controller in such a manner that it would be robust to fairly large model uncertainty with modest computational requirements.